The invention relates to an arc welding system, using a welding wire, preferably a shielded welding wire.
Shielded welding wires are elongated elements (also called  less than  less than electrode greater than  greater than ) including a metallic material adapted for the welding. Typically, the wires comprise a metallic core surrounded by a shield, or a sleeve, with or without a shielding gas useful for the welding (especially an inert gas).
Such so-called  less than  less than shielded wires greater than  greater than  are well known, for example under the reference LINCOR 33 from LINCOLN-USA.
Further, in U.S. Pat. No. 4,672,173, is disclosed a gas-shielded arc welding apparatus for welding rails or shape steel, especially.
Below, the expression  less than  less than rail greater than  greater than  is used to define any weldable article including rail or the like on which a train, tramway . . . can be driven, or any shape steel pertaining to railways.
The apparatus includes a welding torch unit which is provided with a welding wire and which is movable along two different, transversal directions (typically the horizontal and vertical directions).
The apparatus also includes removable fixing means for removably fixing (or crimping) the welding apparatus to the rail  less than  less than and the like greater than  greater than .
Further, torch moving means are included for moving the torch along the above-mentioned transversal directions, and controlling means (such as X-drive block and Y-drive block) connected to the torch moving means are controlling the movement of the welding torch unit in said transversal directions in front of the rail to be welded.
Even if the welding apparatus disclosed in U.S. Pat. No. 4,672,173 is described as a fully-automated apparatus, the welding process can be improved for performing the welding with a higher efficiency, especially in connection with the location of the welding zone on the rail and the like, so that the good or bad welding quality is not (or less) dependent on the skill of the operator, and the weld-time is shorter by less binding the operator to the work during the welding operation.
So, in accordance with one aspect of the invention, the above-mentioned controlling means (or control unit) comprise:
first controlling means for controlling a first movement of the torch unit substantially in front of the periphery (or perimetry) of the zone to be welded, so that welding geometrical locations are recorded (or read) on said zone, by means of recording means connected to a memory unit, so that said welding geometrical locations recorded on the rails are memorized,
and second controlling means for automatically controlling a second displacement of the torch unit in front of the zone to be welded, within the limits of said reading and as a function of the welding geometrical locations, as memorized.
At said locations and at the appropriate rate for obtaining the highest efficiency, the operator is so able to pre-dispose and pre-adjust the displacements the torch unit has to follow for obtaining the welding. Further, memorizing said geometrical location readings and processing the corresponding data enable the operator to fully automatically get the corresponding required welding conditions.
Another object of the invention is to provide a welding process having the above-mentioned advantages.
So, in accordance with one aspect of the invention, the welding process of the invention comprises the steps of:
a) disposing, along at least one rail and the like, an electrical welding apparatus, or robot, using shielded electrically conductive wires adapted for maintaining or repairing rails and the like, the apparatus comprising a torch unit for welding a zone of the rail, a control unit, and fixing means for removably attaching (or crimping) the apparatus to the rail and the like,
b) the torch unit is initially disposed at a referencing (geometrical) location with respect to the zone to be welded,
c) welding geometrical features of said zone are read (or recorded), for obtaining reading (or recording) data,
d) the reading data are addressed to a memory unit, and
e) a determined welding program is initiated, as a function of said addressed reading data, so that:
the torch unit is displaced in front of the zone to be welded, within the limits of said zone, and in accordance with the recorded geometrical features thereof,
the torch unit is provided with a shielded wire, and,
the torch unit is supplied with an electrical power, for welding the rail and the like, as a function of said determined welding program.
An additional problem solved by the invention refers to determining the parameters to be used for the welding, as a function of the true and real situation in the field.
In the invention, two alternative, or cumulative, solutions are proposed:
first of all, prior to step e), the type of shielded wire to be used for the welding operation is selected by means of the control unit among different alternative choices, then the apparatus deduces therefrom:
the feeding rate for feeding the torch unit with said shielded wire,
the supplying power for supplying said torch unit with the electrical power, and
at least during the step e), the displacement rate for displacing the torch unit within the limits of the zone to be welded,
and/or prior to step e), the type of rail to be welded is determined by means of the control unit, among various alternative choices, and then the apparatus deduces from said choice, as a function of the typology of the rail:
the feeding rate for feeding the torch unit with said shielded wire,
the supplying power for supplying said torch unit with the electrical power, and
the displacement rate for displacing the torch unit, within the limits of the zone to be welded.
It is to be noted that adapting the wire features (physico-chemical features, such as the composition thereof) and the feeding rate of the wire within the torch unit, especially, as a function of the rail typology (typically the carbon content of the rails) is often useful.
A further object of the invention is to determine the steps for reading the geometrical features of the zone to be welded, during step c) of the welding process.
The solution which is recommended is as follows:
during step b), the angular position of the torch unit with respect to the zone of the rail to be welded is preferably determined,
during step c), the torch unit is displaced along the edge (or contour) of the welding zone, for reading the welding geometrical features,
then, during step e), further to re-positioning the torch unit at said referencing position, the torch unit is displaced in front of the welding zone, in accordance with the welding program, for depositing a welding material on said welding zone.